Scaling theory for direct current glow discharges predicts that normal discharges can exist at atmospheric pressure in microscale discharge tubes. The validity of this theory is demonstrated by the creation of an atmospheric helium plasma in a nanoliter-size discharge chamber on a microchip. It is shown that the microchip plasma can be successfully applied for molecular emission detection. It exhibits a low detection (10-14 g s-1) limit for methane with a calibration curve that is linear over two decades. Simple instrumentation, small detector size and good sensitivity make the device highly suitable for integration in micro-analysis systems.